Description:
Navigating to the previous slide takes a long time if the previous slide contains pen ink. It takes 12 min or more if the slide contains a non-trivial amount of pen ink. 

The time taken to navigate backwards depends on the amount of ink. Some informal testing on my desktop:
No ink: 0s
1 small line: 0.5s
2 small lines: 0.5s
3 small lines: 1s
4 small lines: 2.5s
5 small lines: 9.5s
6 small lines: 12s

One long line (circled the screen ~2 times): 15 minutes (and counting).

Behaviour occurs 100% of the time, replicated on a 2nd computer.

Steps to Reproduce:
1. Open Impress to a blank presentation (1 blank slide)
2. Begin the slide show.
3. Right-click and select "Mouse Pointer as Pen"
4. Draw a line that goes around the screen twice.
5. Press the right arrow key to advance to the "Click to exit presentation..." slide.
6. Press the left arrow key to return to the slide with the pen ink.


Actual Results:
It takes many minutes to draw the slide with ink.

Expected Results:
It takes <1s to draw slide with ink.


Reproducible: Always


User Profile Reset: No



Additional Info:
While waiting, Impress consumes 8.6% of CPU time on a 12-core system, suggesting it is maxing out one thread.

Clicking on the window, or pressing a key, causes Windows to offer to kill the program or continue waiting.

Version: 7.0.1.2 (x64)
Build ID: 7cbcfc562f6eb6708b5ff7d7397325de9e764452
CPU threads: 12; OS: Windows 10.0 Build 19041; UI render: Skia/Vulkan; VCL: win
Locale: en-US (en_US); UI: en-US
Calc: threaded